Combining fiber enzymatic pretreatments and coupling agents to improve physical and mechanical properties of hemp hurd/wood/polypropylene composite

Abstract

Natural fiber/plastic composites combine the low density and excellent mechanical properties of the natural fiber with the flexibility and moisture resistance of the plastic to create materials tailored to specific applications in theory. Wood/plastic composites (WPC) are the most common products, but many other fibers are being explored for this purpose. Among the more common is hemp hurd. Natural fibers are hydrophilic materials and plastics are hydrophobic, therefore one problem with all of these products is the limited ability of the fiber to interact with the plastic to create a true composite. Thus, compatibilizers are often added to enhance interactions, but fiber pretreatments may also help improve compatibility. The effects of pectinase or cellulase pretreatment of wood/hemp fiber mixtures in combination with coupling agents were evaluated in polypropylene panels. Pretreatments with pectinase or cellulase were associated with reduced thickness swell (TS24h) as well as increased modulus of rupture and modulus of elasticity. Incorporation of 5.0% silane or 2.5% silane/2.5% titanate as a coupling agent further improved pectinase-treated panel properties, but was associated with diminished properties in cellulase treated fibers. Combinations of enzymatic pretreatment and coupling agents enhanced fiber/plastic interactions and improved flexural properties, but the effects varied with the enzyme or coupling agent employed. The results illustrate the potential for enhancing fiber/plastic interactions to produce improved composites.